Diaphragm pressure sensor

ABSTRACT

A pressure sensor includes a diaphragm mounted in relatively fixed relationship with respect to an orifice unit interconnected to the end of a threaded pipe. A threaded adjustment nut is provided with an internal thread to receive the pipe member and includes an outer threaded portion which is threaded into a housing. The inner and outer threads of the adjustment nut are of a very slightly different pitch. The threaded pipe is mounted to prevent rotation of the threaded support member while permitting axial movement thereof. Rotation of the adjustment nut results in axial displacement of the threaded pipe and orifice unit with respect to the diaphragm.

United States Patent Janu Feb. 12, 1974 DIAPHRAGM PRESSURE SENSORPrimary Examiner-Alan Cohan [75] Inventor: George J. Jan, Milwaukee WisAttorney, Agent, or Firm-Andrus, Sceales, Starke &

, Sawall [73] Assignee: Johnson Service Company,

Milwaukee, Wis.

[57] ABSTRACT [22] Flled: 1972 A pressure sensor includes a diaphragmmounted in [21] App]. No.: 284,725 relatively fixed relationship withrespect to an orifice unit interconnected to the end of a threaded pipe.A [52] U S Cl 137/82 threaded adjustment nut is provided with aninternal [5]] i i i i i d 16/00 thread to receive the pipe member andincludes an outer threaded portion which is threaded into a hous- [58]Field of Search 137/82 251/611 265 ing. The inner and outer threads ofthe adjustment nut [56] References Cited are of a very slightlydifferent pitch. The threaded pipe is mounted to prevent rotation of thethreaded UNITED STATES PATENTS support member while permitting axialmovement 3,698,414 10/1972 Nagata 137/85 thereof, Rotation of theadjustment nut results in axial aaulmsmn 235N265 X displacement of thethreaded pipe and orifice unit 2 563 458 2x971 1 71 277 8 with respectto the diaphragm 12 Claims, 5 Drawing Figures I REGULATEQ 4 SUPPLY LOADll 27 W DIAPHRAGM PRESSURE SENSOR BACKGROUND OF THE INVENTION Thisinvention relates to a diaphragm pressure sensor having an adjustableset point control.

In fluid control systems, sensors are often employed to sense pressureconditions within the system and connected to establish an interrelatedcontrol. A highly satisfactory pressure sensor includes an orifice meansconnected to a restricted supply in combination with a diaphragm or lidmeans for adjustably varying the relative opening of the orifice. Thespacing of the orifice from the diaphragm determines the flow andtherefore the back pressure generated within the orifice andinterconnecting supply or fluid line. Generally the unit will includethe diaphragm as a common wall between a reference or input chamber andthe orifice chamber which is also connected to an exhaust or referencepressure. The input chamber may include a calibrated spring incombination with a relatively fine threaded adjustment screw forpreloading of the spring and thereby variably positioning of thediaphragm with respect to the orifice. For any given design, spacers mayalso be introduced between the diaphragm and the support means to adjustthe initial spacing therebetween and thereby the set point adjustment.

The output of the present pressure sensor can provide an essentiallyon-off type output signal by employing diaphragm-leakport amplificationwith a sufficiently high gain.

The pressure sensor may advantageously incorporate the combination of aconvoluted diaphragm and a flat web spring construction in accordancewith the teaching of U. S. Pat. No. 3,662,779 which issued to Weber etal. on May 16, I972. As disclosed therein, the convoluted diaphragmestablishes an essentially zero spring rate while the web spring can beconstructed to produce an essentially constant spring rate to establishan increasing force with displacement in a linear manner.

Although such pressure sensors provide a satisfactory response, the setpoint adjustments require relatively close tolerance adjust meansparticularly if an extremely fine set point adjustment is desired.Further, the prior art sensors have not generally been capable ofsensing extremely low pressures of the order of a fraction of an inch ofwater gauge nor does the set point adjustment encompass a large span.

SUMMARY OF THE PRESENT INVENTION The present invention is particularlydirected to a diaphragm type pressure sensor including an improved setpoint adjustment means which permits the sensing of extremely lowpressures while maintaining accurate setting of the set point pressureover a relatively large span or range. Generally, in accordance with thepresent invention the diaphragm unit is mounted in relatively fixedrelationship with respect to the housing and the orifice unit is movablymounted with respect to the housing to adjust the set point. Inaccordance with a particularly novel aspect of this invention, theorifice means is interconnected into a threaded support member. Athreaded adjustment member is provided with an internal thread toreceive the support member and includes an outer threaded portion whichis threaded into a suitable support housing. The inner and outer threadsof the adjustment member are of a very slightly different pitch.Further, the threaded support member is mounted to prevent rotation ofthe threaded support member while permitting axial movement thereof.Consequently, rotation of the adjustment member results in a very slightaxial displacement of the threaded support member. This permits accuratesetting of the orifice with respect to the diaphragm member.

The diaphragm unit is mounted, preferably with the separate flat spring,with a minimum spring rate at the unstressed mid-position of theassembly and, consequently, its sensitivity is very high at the lowestset point adjustment. Applicant has found that accurate sensing ofrelatively low pressures on the order of a fraction of an inch of watergauge can be obtained with this construction.

The differential threaded arrangement provides for very accurateadjustment of the orifice with relatively inexpensive an readily massproduced components.

In addition the diaphragm and spring assembly can be readily protectedagainst both positive and negative pressure overloads by providingsuitable backing means to the opposite side of the diaphragm surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing furnished herewithillustrates a preferred construction of the present invention and inwhich the above advantages and features are clearly disclosed as well asothers which will be readily understood from the subsequent descriptionof such embodiment.

In the drawing:

FIG. 1 is a vertical section through a pressure sensor constructed inaccordance with the present invention;

FIG. 2 is a horizontal section taken generally on line 2--2 of FIG. 1illustrating an orifice plate interlock construction;

FIG. 3 is an enlarged fragmentary view more clearly illustrating thethreaded construction shown in FIG. 1;

FIG. 4 is a horizontal section taken on line 44 of FIG. I andillustrating the diaphragm construction; and

FIG. 5 is a graphical illustration of the sensor operation.

DESCRIPTION OF ILLUSTRATED EMBODIMENT Referring to the drawing andparticularly to FIG. 1 a flow line I is illustrated with a pressuresensor 2 con.- structed in accordance with the present inventionconnected in line 1. the pressure sensor 2 is shown connected to actuatea load 3 which may, for example, be a timing portion of a controllersuch as disclosed in Applicants co-pending application entitled TWO-POSITION LIQUID LEVEL CONTROLLER, which was filed on the same day asthis application and is assigned to a common assignee with thisapplication. The pressure sensor 2 is a leakport type unit connected toa regulated fluid supply 4 via a pressure dropping restrictor 5. Theload 3 is connected between the restrictor 5 and the pressure sensor 2.The restrictor 5 and the pressure sensor 2 define a pressure dividingnetwork with the pressure signals applied to the load 3 being directlycontrolled by the flow through the pressure sensor 2 and the resultingpressure drop on the orifice 5.

The pressure sensor 2 includes a passageway 6 terminating in an orifice7. A diaphragm unit 8 forms a part of an input chamber 9 and is mountedin overlying spaced relationship to the orifice 7. The member 9 formsone part of a two piece housing and is threaded into a mounting stub onthe flow line 1 to interconnect the sensor 2 to the flow line. Thus, thepressure in the flow line 1 is developed to the underside of thediaphragm unit 8, in the illustrated embodiment of the invention, andcorrespondingly positions the diaphragm unit to adjust the exhaust flowfrom the orifice 7.

The orifice 7 terminates within a discharge chamber 11 formed within theopposite housing member 12 and is connected via a discharge passageway13 to a suitable reference pressure as by a connecting conduit 14. Thepassageway may, of course, be directly exited to atmosphere forpneumatic systems and the like. If the apparatus is to be operatedsubmerged in liquid or the like the conduit 14 can, of course, providefor exiting to an appropriate atmosphere or other enviornment.

More particularly in the illustrated embodiment of the invention, thepassageway 6 is formed in and as a part of a threaded screw 15 whichdefines a threaded support member for the orifice 7. The upper end ofthe screw 15 is provided with a suitable connector 16 for connection tothe load 3 and the restrictor 5.

The member 15 is threaded into an adjustment nut 17 by correspondingthreads as at 18. The adjustment nut 17, in turn, is threaded into anappropriately tapped opening in the housing 12 as at 19.

The threaded screw 15 includes an inner smooth shaft 20 which extendsdownwardly through an unthreaded portion of nut 17 and a reduced throatsection 21 in the housing 12 immediately above the chamber 1 1. AnO-ring seal 22 seals the throat 21 about the shaft portion 20. The innerend of the screw 15 is enlarged to define an orifice plate 23 which isgenerally a discshaped member with the orifice 7 formed as a nozzleprojection from the lower wall thereof which terminates in lower flatface 24. Referring particularly to FlGS. l and 2, the peripheral edge ofthe plate 23 is provided with a plurality of axial notches shown as afirst pair of diametrically located notches 25 and 26 and a second setof diametrically located notches 27 and 28 displaced 90 with respect tothe first pair. A locking ring 29 is secured as by a suitableinterconnecting adhesive or attachment means 30 to the side wall of thechamber 11. It includes a pair of diametrically inwardly radialprojections 31 and 32 aligned and mating with the diametrical slots 27and 28 in the plate 23. The slots 27 and 28 and mating projections 31and 32 prevent rotation of the screw 15. The notches extend throughoutthe depth of the plate 23, however, and thus permit axial movement ofthe orifice plate 23 and interconnected screw 15.

In accordance with a particularly novel aspect of the present invention,the threads 17 and threads 18 are of a slightly different pitch, asshown in the enlarged view of FIG. 3 at 33. Consequently, rotation ofthe threaded nut 17 in combination with the prevention of the rotationof the screw 15 establishes a differential screw action causing thescrew 15 and interconnected orifice plate 23 to move a slight amount forangular rotation of the adjustment member 17. In this manner the orifice7 is accurately and finely located with respect to the diaphragm unit 8.

The diaphragm unit 8 is preferably constructed in accordance with thepreviously referred to issued patent of Weber et al. in particular, thediaphragm unit 8 includes a flat, web spring 34 and a highly flexibleconvoluted diaphragm 35 which are clamped completely about theperipheral edge between the housing members 9 and 12 with the centralportion thereof coaxially aligned with the orifice 7. An encirclingconvolution 36 is formed in the diaphragm and projects into the inputchamber defined by the housing 9. The diaphragm has an essentially zerospring rate as the result of the convolution. The web spring 34 isprovided with a peripheral annular mounting portion 37 which isconnected to a central ring portion 38 by a plurality of curved leafspring arms 39. The inner ring portion 38 exposes the diaphragm 35 tothe orifice 7 to permit movement of the diaphragm into sealingengagement with the orifice face 24. The engagement, however, of theannular ring 38 with the orifice plate 23 will support the spring memberand prevent excessive deflection in the event of significant positivepressures within'the input chamber 9. The diaphragm 35 is furtherpreferably constructed with an inwardly projecting integral enlargement40 in the central portion within the convolution 36. A diaphragmpressure stop 41 is supported by a bridging bracket 42 which spans themember 9 and is secured at the opposite ends to the member 9. The stop41 is thus located in slightly spaced relation to the enlargement 40 andis engaged thereby in the event of an abnormal negative pressurecondition in the input chamber.

The set point adjustment of sensor 2 is obtained by axially positioningof the orifice 7 with respect to the unit 8 with the diaphragm andspring in the midposition. If the orifice 7 is positioned inwardly inclosely spaced relation to the diaphragm assembly 8, a very slightpressure in the input chamber will result in a movement into effectivesealing engagement over the orifice, thereby rapidly establishing anincreased back pressure generally corresponding to the regulated supplypressure. Conversely, as the orifice 7 is retracted as the result ofrotation of the threaded adjustment member 17, the spacing is increasedand the input pressure must rise to a correspondingly increased levelbefore effecting a closure of the orifice.

The mid-position of the spring which is established with a zero inputpressure signal in the input chamber is also the position of thesmallest spring rate. As the spring is deflected, the spring rateincreases thereby providing for the highest sensitivity of the sensor atthe low set-point adjustments and at the same time for a wide span ofset-point adjustment.

Thus, typical characteristics are shown in FIG. 5 for various positiveand negative pressures from a regulated supply. The outputcharacteristic for a positive supply are shown in the first quadrant andthose for a negative supply in the fourth quadrant. For practicalpurposes, the output signal corresponding to the maximum positive ornegative signal level are in a fully on state equal to the supplypressure while atmospheric or reference zero pressure represents a fullyoff state.

In a practical application as specifically constructed for the vacuumpowered sewage transport system, the diaphragm was formed of an EPTrubber with a 0.775 inch effective diameter. The diaphragm was supportedby a pair of web springs formed of a 0.005 beryllium copper defining atotal average spring rate of approximately 9.4 pounds per inch. Theorifice was supported by a screw having threads of the standard 10-32UNF and an adjustment nut member having an external thread of 5/ 16-30UNS. The threaded arrangement established a leakport displacement ofessentially 0.0021 inches per complete turn of the adjusting thread nutmember. This is equivalent to a single screw with approximately 476threads per inch.

The adjustable set point permitted variation between zero and 36 inchesof water gauge as a result of approximately turns of the adjusting nutmember. The system operated with a nominal supply of fifteen inches ofmercury vacuum. This sensor operated satisfactorily submerged in waterand could readily withstand positive pressure overloads in the inputchamber of up to 25 pounds per square inch gauge and negative pressureswithin the control chamber of the order of 25 inches of mercury vacuumwhile maintaining a set point deviation of plus and minus 5 percent.

The present invention thus provides an adjustable set point leakporttype sensor which permits sensing of very low pressures while having anextremely fine set point adjustment, without the necessity of componentswhich are difficult or expensive to manufacture. The sensor can beemployed with either a positive or negative pressure source and thesupply magnitude can be adjusted to suit the need of the givenapplication.

I claim:

1. An adjustable leakport pressure sensor employing a leakport means andpressure responsive closure means having a predetermined positionrelative to the leakport means for opening and closing of the leakportmeans to establish essentially full pressure and reference pressure,comprising an input chamber means, an orifice unit, a rotatableadjustment member threadedly mounted within the input chamber portionand having a threaded opening aligned with the orifice unit, saidorifice unit having a threaded support portion threaded into saidthreaded opening, the inner threads and outer threads of said adjustmentmember having slightly different pitches, and means coupled to saidorifice unit permitting axial movement of the threaded support portionrelative to predetermined position of the closure means and preventingrotation of the threaded support portion to establish a setpoint controlof the pressure sensor.

2. The pressure sensor of claim 1 wherein the difference in said threadpitch is of the order of one thou sandths of an inch.

3. The pressure sensor of claim 1 wherein the difference in said threadpitch is between one and four thousandths of an inch.

4. An adjustable pressure sensor apparatus comprising a housing memberhaving a flexible diaphragm wall means defining a portion of a controlchamber and of an input chamber, an adjustment nut threaded into saidhousing with an axis normal for said flexible wall means, an adjustmentscrew threaded into said nut and having an inner nozzle means locatedwithin said control chamber with an end orifice in opposed relation tosaid flexible wall means and opened and closed thereby to establish fullpressure and reference pressure in the control chamber in response toslight movement of the wall means, interlock means coupling said nozzlemeans to said housing and preventing rotation of said screw and havingmeans permitting axial movement of said screw, said adjustment nutincluding inner and outer threads of slightly different thread pitch tomove the nozzle in response to rotation of the nut.

5. The pressure sensor of claim 4 wherein said flexible wall meansincludes a resilient diaphragm of a rubber-like material rigidly clampedabout the periphery and with a flat planar sealing face aligned with theorifice, said diaphragm having an essentially zero spring rate in thediaphragm, and a flat spring clamped against said diaphragm between saidorifice and said diaphragm, said spring including a center ring portionconcentric of said orifice and connected to an outer ring portion by aplurality of spring arms to establish a preselected diaphragm springrate.

6. The sensor of claim 5 having a stop wall located in the input chamberin alignment with the center of the diaphragm.

7. The pressure sensor of claim 4 wherein said flexible wall meansincludes a resilient diaphragm of a rubber-like material rigidly clampedabout the periphery and with a flat planar sealing face aligned with theorifice, said diaphragm having a convolution projecting into the inputchamber, said convolution establishing an essentially zero spring ratein the diaphragm, a flat spring clamped against said diaphragm betweensaid orifice and said diaphragm, said spring including a center ringportion concentric of said orifice and connected to an outer ringportion by a plurality of spring arms to establish a preselecteddiaphragm spring rate, and a stop wall located in the input chamber inalignment with the center of the diaphragm.

8. The sensor apparatus of claim 4 having a regulated fluid supply meansconnected to establish flow through said orifice in accordance with theposition of said wall, and a load connection means connected to saidorifice to respond to the back pressure resulting from the position ofthe diaphragm wall means.

9. The pressure sensor of claim 4 wherein said housing includes acontrol member having a central threaded opening to receive said nut anda recess in one end defining said control chamber with a sidewallconnecting passageway to said control chamber, an intermediate sectionconnecting said control chamber to the threaded opening, said screwhaving a smooth shaft portion aligned with said intermediate section, aseal rotatably sealing the section about the shaft portion, said nozzleand interlock means including a plurality of axial notches and matingprojections extending into said notches, said notches being longer thansaid projections to permit said axial movement of said screw.

10. The pressure sensor of claim 4 wherein said housing includes acontrol member having a central threaded opening to receive said nut anda recess in one end defining said control chamber with a sidewallconnecting passageway to said control chamber, a reduced throat sectionconnecting said control chamber to the threaded opening, said screwhaving a smooth shaft portion aligned with said throat section, anO-ring seal rotatably sealing the throat section about the shaftportion, said enlarged nozzle having a plurality of outer axialperipheral notches, and said interlock means ineluding selected notchesless than all of said notches and a ring member attached to the adjacentwall of the control chamber with interlock projections extending intosaid selected notches.

11. An adjustable set point pressure sensor employing a leakport means apressure responsive closure means for variably opening and closing ofthe leakport means, comprising a input chamber means, an orifice unit, ahousing for said orifice unit, means to mount said closure means in saidinput chamber to establish a relatively fixed position relative to saidhousing, and movable adjustment means connected to said orifice unit andmovable axially of the orifice unit and reposi- 1 wherein said closuremeans includes a convoluted flexible diaphragm wall means having anessential zero spring rate and a flat web spring having its lowestspring rate at the unstressed mid-position of the closure v 11 UNITEDSTATES PATENT 5mm CERTIFICATE OF CORRECTION Dated ebruary 12, 1974Patent No. 3,791,397

Invent r( )George .I. Janu It is certified that error appears in theabove-identified patent and that said Letters Patentare herebycorrectedas shown below:

Claim 4, line 51, helical "for" and substitute therefor '-to---- Sigried end sealed this 17th day of December 974.

(SEAL) Attest: v

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of-Patents RM PO-1050 (10-65)

1. An adjustable leakport pressure sensor employing a leakport means andpressure responsive closure means having a predetermined positionrelative to the leakport means for opening and closing of the leakportmeans to establish essentially full pressure and reference pressure,comprising an input chamber means, an orifice unit, a rotatableadjustment member threadedly mounted within the input chamber portionand having a threaded opening aligned with the orifice unit, saidorifice unit having a threaded support portion threaded into saidthreaded opening, the inner threads and outer threads of said adjustmentmember having slightly different pitches, and means coupled to saidorifice unit permitting axial movement of the threaded support portionrelative to predetermined position of the closure means and preventingrotation of the threaded support portion to establish a setpoint controlof the pressure sensor.
 2. The pressure sensor of claim 1 wherein thedifference in said thread pitch is of the order of one thousandths of aninch.
 3. The pressure sensor of claim 1 wherein the difference in saidthread pitch is between one and four thousandths of an inch.
 4. Anadjustable pressure sensor apparatus comprising a housing member havinga flexible diaphragm wall means defining a portion of a control chamberand of an input chamber, an adjustment nut threaded into said housingwith an axis normal for said flexible wall means, an adjustment screwthreaded into said nut and having an inner nozzle means located withinsaid control chamber with an end orifice in opposed relation to saidflexible wall means and opened and closed thereby to establish fullpressure and reference pressure in the control chamber in response toslight movement of the wall means, interlock means coupling said nozzlemeans to said housing and preventing rotation of said screw and havingmeans permitting axial movement of said screw, said adjustment nutincluding inner and outer threads of slightly different thread pitch tomove the nozzle in response to rotation of the nut.
 5. The pressuresensor of claim 4 wherein said flexible wall means includes a resilientdiaphragm of a rubber-like material rigidly clamped about the peripheryand with a flat planar sealing face aligned with the orifice, saiddiaphragm having an essentially zero spring rate in the diaphragm, and aflat spring clamped against said diaphragm between said orifice and saiddiaphragm, said spring including a center ring portion concentric ofsaid orifice and connected to an outer ring portion by a plurality ofspring arms to establish a preselected diaphragm spring rate.
 6. Thesensor of claim 5 having a stop wall located in the input chamber inalignment with the center of the diaphragm.
 7. The pressure sensor ofclaim 4 wherein said flexible wall means includes a resilient diaphragmof a rubber-like material rigidly clamped about the periphery and with aflat planar sealing face aligned with the orifice, said diaphragm havinga convolution projecting into the input chamber, said convolutionestablishing an essentially zero spring rate in the diaphragm, a flatspring clamped against said diaphragm between said orifice and saiddiaphragm, said spring including a center ring portion concentric ofsaid orifice and connected to an outer ring portion by a plurality ofspring arms to establish a preselected diaphragm spring rate, and a stopwall located in the input chamber in alignment with the center of thediaphragm.
 8. The sensor apparatus of claim 4 having a regulated fluidsupply means connected to establish flow through said orifice inaccordance with the position of said wall, and a load connection meansconnected to said orifice to respond to the back pressure resulting fromthe position of the diaphragm wall means.
 9. The pressure sensor ofclaim 4 wherein said housing includes a control member having a centralthreaded opening to receive said nut and a recess in one end definingsaid control chamber with a sidewall connecting passageway to saidcontrol chamber, an intermediate section connecting said control chamberto the threaded opening, said screw having a smooth shaft portionaligned with said intermediate section, a seal rotatably sealing thesection about the shaft portion, said nozzle and interlock meansincluding a plurality of axial notches and mating projections extendinginto said notches, said notches being longer than said projections topermit said axial movement of said screw.
 10. The pressure sensor ofclaim 4 wherein said housing includes a control member having a centralthreaded opening to receive said nut and a recess in one end definingsaid control chamber with a sidewall connecting passageway to saidcontrol chamber, a reduced throat section connecting said controlchamber to the threaded opening, said screw having a smooth shaftportion aligned with said throat section, an O-ring seal rotatablysealing the throat section about the shaft portion, said enlarged nozzlehaving a plurality of outer axial peripheral notches, and said interlockmeans including selected notches less than all of said notches and aring member attached to the adjacent wall of the control chamber withinterlock projections extending into said selected notches.
 11. Anadjustable set point pressure sensor employing a leakport means apressure responsive closure means for variably opening and closing ofthe leakport means, comprising a input chamber means, an orifice unit, ahousing for said orifice unit, means to mount said closure means in saidinput chamber to establish a relatively fixed position relative to saidhousing, and movable adjustment means connected to said orifice unit andmovable axially of the orifice unit and repositioning of the orificeunit without rotation of said orifice unit in response to movement ofthe adjustment means and axially adjusting the position of the orificeunit accurately with respect to said housing to adjust the set point ofthe sensor.
 12. The adjustable set point pressure sensor of claim 1wherein said closure means includes a convoluted flexible diaphragm wallmeans having an essential zero spring rate and a flat web spring havingits lowest spring rate at the unstressed mid-position of the closuremeans.